Carbon black obtained from aqueous suspensions

ABSTRACT

This invention relates to carbon black obtained from an aqueous suspension. A practically water-free carbon black is obtained from aqueous suspensions by mixing the suspension with liquid low-boiling hydrocarbons, then expanding the mixture in a vessel to evaporate the hydrocarbons, then drawing off separately the hydrocarbon vapors carrying the carbon black and the remaining liquid aqueous phase from the vessel, and separating the carbon black from the hydrocarbon vapors.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention is a continuation-in-part application ofapplication Ser. No. 212,363, filed Dec. 3, 1980, now U.S. Pat. No.4,329,329, granted May 11, 1982.

BACKGROUND OF THE INVENTION

The present invention relates to a carbon black obtained from an aqueoussuspension by mixing the suspension with low-boiling hydrocarbons, thenexpanding the mixture into a vessel, whereby the mixture separates intoa gas phase of the hydrocarbon vapors which form during expansion andcarry the carbon black, and into an aqueous liquid phase, and recoveringthe carbon black from the gas phase.

It is known to hydrophobisize carbon black suspended in water, asproduced, for example, in oil-pressure gasification processes, byadmixing hydrocarbons, which causes the carbon black to separate fromthe water. The general purpose of this process is to resupply theseparated carbon black to the gasification reactor and to reuse thewater freed from carbon black in the process in which thecarbon-black-water-suspension is produced. In these cases, it isappropriate to carry out hydrophobisization directly with heavyhydrocarbon oils, e.g. using heavy fuel oils or crude oil vacuumresidues. Since the separation process is relatively slow when mixingwith heavy oils, even if the process is carried out at elevatedtemperatures, it has proved successful to carry out hydrophobisizationusing low boiling hydrocarbons and in a second stage, to mix the carbonblack-hydrocarbon-suspension with a heavy oil. After the lighthydrocarbons have been separated by distillation, the suspension maythen be returned to the gasification installation. If, however, thecarbon black is to obtain as such, then, according to the prior art, thesuspension of carbon black in liquid hydrocarbons is separated from thecarbon black-free water and the hydrocarbon is separated mechanically orby evaporation.

The carbon black obtained in this manner still contains large quantitiesof water, e.g. as much as 15% (DT OS No. 2,216,155), and even moreaccording to the method of recovering, e.g. from 40 to 70% (DT OS No.2,510,876). If carbon black having a lower water content is required,then an expensive drying process must be carried out subsequently whichgenerally takes place at temperatures of from 35° to 600° C.

In a process recently described carbon black may be obtained fromaqueous carbon black suspensions having a water content of onlyapproximately 2% by weight. This is achieved by treating the aqueouscarbon black suspension with low-boiling hydrocarbons at elevatedpressure and then expanding the mixture, during which expansion, aseparation into evaporated hydrocarbons, water which is extensivelyfreed from carbon black and carbon black takes place (DT OS No.2,546,072).

SUMMARY OF THE INVENTION

According to the present invention a dry, non-adhesive carbon blackhaving an even lower water content compared with the process describedabove is obtained from an aqueous suspension, when the suspensioncontaining the carbon black is mixed with liquid low-boilinghydrocarbons, then the mixture is expanded at a temperature of from 20°to 180° C. and at a pressure of from 2 to 30 bars in a vessel to apressure lower than that of the mixture, then the gaseous phase of theevaporated hydrocarbons, formed during expansion and carrying the carbonblack and the remaining liquid aqueous phase, being substantially freeof carbon black are drawn off separately from the expansion vessel, andthe carbon black is separated from the hydrocarbon vapors.

A loop with a mixing pump is advantageously used for mixing the carbonblack-water-suspension and the hydrocarbons, but other mixing members,e.g. an impeller-type mixer, may also be used. The low-boilinghydrocarbons which are to be admixed have appropriately from 3 to 10,and advantageously from 4 to 8 carbon atoms. The following are mentionedas examples: butane, pentane, hexane, benzene, and also benzenefractions of corresponding boiling ranges. The mixing operation takesplace, according to the selected hydrocarbons, at from 20° to 180° C.and at a pressure of from 2 to 30 bars. If pentane or hexane is used,mixing is carried out, for example, at from 4 to 8 bars and from 60° to100° C. The mixture of carbon black, water and hydrocarbon is expandedin a vessel which is at a lower pressure than that of the mixingapparatus. Expansion must be effected such that, for example, by using apump, the hydrocarbon-water-carbon black system is thereby preventedfrom separating into its components. Such a separating should not occuruntil downstream of the expansion apparatus. Expansion is generallycarried out to normal pressure, but the expansion vessel may naturallyalso be operated at a higher or lower pressure, as long as there is anadequate pressure drop between it and the mixing apparatus. Theexpansion vessel is maintained at a temperature which suffices to allowthe hydrocarbon used, but not the water to evaporate. This temperatureis generally from 80° to 120° C. The carbon black is removed with thehydrocarbon vapors from the expansion vessel. In a preferred embodiment,a down pipe is positioned in the expansion vessel, which pipe projectshigh enough above the aqueous phase so that the evaporated hydrocarbonsare drawn off together with the carbon black through the down pipewithout portions of the aqueous phase passing into the down pipe. It isnaturally also possible to remove hydrocarbon vapors and carbon black inanother way from the expansion vessel. The aqueous phase, produced inthe vessel and being practically free of carbon black is advantageouslyremoved from the lower region of the vessel. It may, for example, bereturned into the apparatus for the production of the carbon blacksuspension or may be introduced into an oil gasification installation asquench water.

The carbon black is separated in known manner from the carbonblack-hydrocarbon vapor mixture. Thus, the down pipe may open into acyclone or centrifugal separator where the carbon black separation takesplace. It may be appropriate to subsequently purify the hydrocarbonvapors leaving the cyclone, for example, by a second cyclone and/or awash. This may be effected, for example, using hot high-boilinghydrocarbon oils which may then be used as a charging material forgasification. Instead of cyclones, other conventional separating devicesmay be used, for example filters, and also combinations of a cyclone anda filter. The carbon black is separated at elevated temperatures, forexample, from 80° to 120°. The hydrocarbon vapors free of carbon blackmay, for example, be returned after condensation into the mixingapparatus.

The carbon black leaving the expansion vessel with the hydrocarbonvapors generally has a water content of approximately from 0.5 to 1.5%by weight. This content may be reduced by introducing the carbon blackinto a drying installation after being separated from the hydrocarbonvapors. In this case, in a known manner, for example by heating or bytreating with hot inert gases, the water content may be reduced evenfurther. A particular advantage of the process according to theinvention is that the drying may be effected at relatively lowtemperatures, for example at from 200° to 300° C. The carbon black whichis thus obtained is water-free, non-adhesive and outstandingly storable.

The carbon black is dry, non-adhesive, and has a nitrogen surface area(ASTM D 3037-78) in the range of 750-1050 m² /g, and a DBP absorption(ASTM D 2414-79) in the range of 380-420 ml/100 g. The particle diameteras determined by electron microscope is about 30 NM.

BRIEF DESCRIPTION OF THE DRAWING

Novel features and advantages of the present invention in addition tothose mentioned above will become apparent to one skilled in the artfrom a reading of the following detailed description in conjunction withthe accompanying drawing wherein similar reference characters refer tosimilar parts and in which:

The process for producing the carbon black of the invention isrepresented by way of example in a simplified manner with reference tothe single FIGURE of the drawing which is a schematic flow diagram ofone embodiment of this invention.

DETAILED DESCRIPTION OF THE INVENTION

Into a mixing apparatus 2 which is maintained at an elevatedtemperature, a carbon black-water suspension at elevated pressure isintroduced via line 1 and a low-boiling hydrocarbon fraction at the samepressure is introduced via line 28. The mixture is passed into a heatedexpansion vessel 4 which is at normal pressure via an expansion device3. In the expansion vessel 4, separation occurs into an aqueous liquidphase, which is removed from the process via line 6 and into a gaseousphase from the hydrocarbon vapors which also carry the carbon black andflow into a cyclone 8 via a down pipe 5, in expansion vessel 4 extendingthrough the collected liquid aqueous phase, and through a line 7. Thecyclone or centrifugal separator 8 is maintained at approximately thesame temperature as the vessel 4. The carbon black separated in thecyclone 8 passes via line 9 into a dryer 10, onto which nitrogen isintroduced via line 24. The dried, water-free carbon black is passedinto a bin 12 via line 11.

The hydrocarbon vapors, freed from carbon black in the cyclone 8, passvia line 13 into a washer 14 maintained at an elevated temperature wherethey are washed with heavy oil supplied via line 15, in order to removefrom them the last traces of carbon black. The heavy oil used is removedfrom the process via line 16. The hydrocarbon vapors are introduced intoa condenser 18 via line 17 and, after condensation, pass via line 19into a container 20 with a column 21 in which there is reflux of thecondensed hydrocarbon fraction throughout line 25. This is separatedfrom the nitrogen which is introduced. The nitrogen passes via a cooler22 and line 24 as an inert gas after being heated (not shown) into thedryer, optionally also into the bin 12. If the inert gas is not requiredhere, it is removed from the process via line 23. The hydrocarbonfraction leaves the container 20 via line 26, is brought to thenecessary pressure in a pump 27 and passes into the mixing apparatus 2via line 28.

    __________________________________________________________________________                  NITROGEN             PARTICLE                                                 SURFACE AREA                                                                            DBP ABSORPTION                                                                           DIAMETER                                   CARBON BLACK  (m.sup.2 /g)                                                                            (ml/100 g) (NM)                                       __________________________________________________________________________    Present Invention                                                                           750-1050  380-420    30                                         Super Abrasion Furnace                                                                      125-155   113        18                                         High Abrasion Furnace                                                                       70-90     102        30                                         Medium Processing Channel                                                                   105-125    96        24                                         Medium Thermal*                                                                             6-9        39        300                                        General Purpose Furnace                                                                     26-42      91        55                                         High Color Channel                                                                          1000      475        10                                         Acetylene Black                                                                              65       320        40                                         __________________________________________________________________________     *"Medium Thermal" means slow thermal decomposition of hydrocarbons in hot     chambers.                                                                

The above table shows that the carbon black of the present invention isa new type which combines very high surface area and DBP-absorption withan unusually high particle diameter. Compare, for example, the carbonblack of the present invention with the high color channel carbon black.This means that by adding a certain amount of weight of carbon black ofthis invention, for example, to a plastic material a composition isobtained which exhibits unusually high electric conductivity becauserelatively large areas of the composition consist of non-interruptedcarbon black-zones. As a result, the present carbon black is highlysuitable for applications like video records with electric scanner.Furthermore carbon black-plastic compositions of this type carry noelectrostatic charge, which is for example very important in the case ofgasoline tanks.

The grit-content of the present carbon black is practically zero. Thisis a consequence of the separation of the carbon black from the watersuspension with the hydrocarbon vapor. Grit means particles withdiameters larger than 45×10-6 m which are mostly non-carboncontaminations like ash and metal oxides. In many applications theabsence of grit is very important leading to new applications, forexample, video records.

The present carbon black has the further advantage that metal-traceswhich are smaller than 45×10-6 m are reduced, the same way as gritparticles do, to a low content. This way, for example, the vanadiumconcentration lowers in the present carbon black to about half the levelin comparison to other processes where the ash is not separated.

Example

50 m³ /h of an aqueous carbon black suspension, containing 0.8% byweight of carbon black, were mixed with 3 t/h of a low-boilinghydrocarbon fraction at 80° C. and 6 bars and were then expanded in avessel which was maintained at approximately 80° C. and at normalpressure.

The carbon black leaving the expansion vessel with the hydrocarbonvapors contained 0.7% by weight of water. The water removed from thevessel was practically free of carbon black. The carbon black wasseparated from the hydrocarbon vapors in a cyclone at approximately 110°C. The carbon black was subsequently dried at approximately 275° C., andwas then practically water-free.

We claim:
 1. Carbon black obtained from an aqueous suspension by theprocess of mixing the aqueous suspension containing carbon black withliquid low-boiling hydrocarbons having from 3 to 10 C-atoms, thenexpanding the mixture in a single expansion step into a vessel which isat a lower pressure than that of the mixture without separating thecomponents of the mixture, the single expansion step being carried outat a temperature of from 20° to 180° C. and at a pressure of from 2 to30 bars in such a manner that the hydrocarbons are evaporated into agaseous phase carrying the carbon black but only after expansion, thendrawing off separately the gaseous phase of the evaporated hydrocarbonsformed after expansion and carrying the carbon black, and the remainingliquid aqueous phase which is substantially free of carbon black fromthe expansion vessel, and separating the carbon black from thehydrocarbon vapor, the carbon black having a nitrogen surface area inthe range of 750-1050 m² /g, and a DBP absorption in the range of380-420 ml/100 g and wherein the particle diameter is approximately 30nm.
 2. Carbon black as in claim 1 having a low ash content.